Sow early in the low rainfall zones
GroundCover™ Issue: 5
Sow early, direct-drill, and choose a variety according to the timing of the seasonal break. These are the recommendations from GRDC-funded trials by the Department of Agriculture, Western Australia, applicable to low rainfall zones.
At the start- of this" project, farmers in low rainfall areas of Western Australia usually delayed seeding for one to three weeks after the break of the season. This delay is not optimal for yield because with later sowing, wheat yields are restricted by water shortages during grain filling. Farmers had traditionally sown later than the optimum time for a number of reasons:
- risk of frost damage
- leaf diseases
- problems controlling weeds during seedbed preparation
- lack of suitable later-maturing varieties. By the late 1980s, new information available to researchers prompted a rethink of these strategies.
Frost. Frost risk in the north-eastern wheatbelt of Western Australia is in fact very low. Frost risk should be well-known to most farmers.
Leaf disease. The most common leaf diseases in the regions of interest are yellow spot and Seproria nodorum blotch. While agreeing that early sowing exposes wheat to greater disease risk, scientists felt that it might still be worthwhile, except in the wettest regions.
Weed control. Advances in chemical weed control (pre- and post-emergence) have reduced one of the major practical problems associated with early sowing, although brome grass and barley grass were still a concern. Other grass weed management methods looked promising.
New varieties. New varieties such as Spear and Machete can be sown early without the risk of prematurely 'running up into head'.
Direct drilling. Improvements in direct drilling techniques offered the prospect of removing the one- to three-week delay between seasonal break and sowing.
Sowing date and cultivar
Sowing between mid-May and early June produced the highest grain yield. For plantings after early June, yields declined by about 15 per cent per week Delayed sowing reduced plant growth and kernel number on a unit area basis. Usually, kernel weight did not rise in compensation for the fall in number.
Time of sowing did not influence grain protein or the amount of screenings. Hectolitre weight did increase with later sowing, but even at early sowing it usually remained above 74 kg/hl, the test weight minimum delivery standard.
From early sowing, medium- and long-season varieties yielded best. Short-season types performed better after delayed sowing. The researchers recommend that farmers retain a number of wheat varieties with a range of maturities suited to a range of planting times.
Crop establishment techniques
A sowing delay of 10-14 days beyond the optimum date reduced yield by 24. per cent on average. Since direct drilling performed as well as other methods, it is the best choice on the medium-heavy textured soils in the low rainfall zone because it allows earlier sowing.
Rainfall patterns and varietal choice
Farmers in the WA north-eastern wheatbelt are able to sow before May 10 in about one year in three. If they do not get that opportunity, the wait before the next suitable rains can often be 30-55 days. This has important implications for the varieties they keep on hand. Long season varieties (e.g. Spear) are useful in some years in the drier regions, but should be only a small part of seed retained. Most of it should be mid- to short-season types, with maturities similar to Eradu and Gutha.
Region National, North, South, West